Methacrylic resin, shaped article, and optical component or automotive part

1. A methacrylic resin,

the methacrylic resin having a cyclic structure in a main chain thereof,

the methacrylic resin having a glass transition temperature of higher than 120° C. and 160° C. or lower,

wherein a sign of an orientational birefringence when being oriented so as to have a degree of orientation of 0.03 is different from the sign of the orientational birefringence when being oriented so as to have a degree of orientation of 0.08.

2. The methacrylic resin according to claim 1 , wherein

an absolute value of the orientational birefringence when being oriented so as to have a degree of orientation of 0.03 is 0.1×10 −5 or more and 5.0×10 −5 or less, and

the absolute value of the orientational birefringence when being oriented so as to have a degree of orientation of 0.08 is 8.0×10 −5 or less.

3. The methacrylic resin according to claim 2 , wherein

the absolute value of the orientational birefringence when being oriented so as to have a degree of orientation of 0.03 is 0.1×10 −5 or more and 3.0×10 −5 or less, and

the absolute value of the orientational birefringence when being oriented so as to have a degree of orientation of 0.08 is 5.0×10 −5 or less.

4. A methacrylic resin,

the methacrylic resin having a structural unit having a cyclic structure in the main chain thereof,

the methacrylic resin having a glass transition temperature of higher than 120° C. and 160° C. or lower,

wherein a difference in an abundance ratio of the structural unit having the cyclic structure in the main chain thereof is 3.0 mass % or less between a fraction component having a peak top molecular weight of 40,000 to 50,000 and a fraction component having a peak top molecular weight of 240,000 to 260,000, the fraction components being obtained through a molecular weight fractionation.

5. The methacrylic resin according to claim 4 , wherein

an absolute value of a difference between an absolute value of an orientational birefringence when being oriented so as to have a degree of orientation of 0.03 and the absolute value of the orientational birefringence when being oriented so as to have a degree of orientation of 0.08 is 5.0×10 −5 or less.

6. The methacrylic resin according to claim 4 , wherein

the absolute value of the orientational birefringence when being oriented so as to have a degree of orientation of 0.03 is 0.1×10 −5 or more and 5.0×10 −5 or less, and

the absolute value of the orientational birefringence when being oriented so as to have a degree of orientation of 0.08 is 8.0×10 −5 or less.

7. The methacrylic resin according to any one of claims 1 to 6 , wherein a yellowness index (YI) of a molded piece produced by injection molding the methacrylic resin measured in an optical path length of 80 mm is 20 or less.

8. The methacrylic resin according to any one of claims 1 to 6 , wherein the methacrylic resin has a photoelastic coefficient of −3×10 −12 to +3×10 −12 Pa −1 .

9. The methacrylic resin according to any one of claims 1 to 6 , wherein the methacrylic resin comprises an N-substituted maleimide monomer-derived structural unit.

10. The methacrylic resin according to any one of claims 1 to 6 , wherein the methacrylic resin comprises a glutarimide structural unit.

11. A shaped article comprising the methacrylic resin according to any one of claims 1 to 6 , or a methacrylic resin composition comprising the methacrylic resin according to any one of claims 1 to 6 .

12. The shaped article according to claim 11 , wherein the shaped article has a thickness of 1.5 mm or less.

13. An optical component or an automotive part comprising the shaped article according to claim 11 .